1. Field of the Invention
The present invention relates to a lens barrel provided with a lens drive apparatus structured so that 2 lens groups are moved by a single drive source, and an image pick-up apparatus provided with the lens barrel.
2. Description of the Related Art
Conventionally, cameras mounted with a photographic lens whose focal distance can be changed (hereinafter, called also zoom lens) come into the market. The zoom lens is structured in such a manner that a change of the focal distance (zooming) is conducted when a plurality of lens groups composing an optical system are moved to a desired position along the optical axis, and the interval is changed.
As methods for moving the plurality of lens groups along the optical axis, there are 2 kinds which are largely separated, one of which is the lens frame is engaged with a go-straight guide, and when a cam cylinder is rotated, the lens frame is go-straight moved, and the other one of which is structured in such a manner that an axis is arranged almost in parallel to the optical axis and this axis is used as a guide axis for go-straight guide, and a sleeve through which the guide axis is penetrated into the lens frame is formed, and by using a motor and a lead screw, the lens frame is directly slidingly moved along the guide axis and straightly go-moved.
As the former system by which the lens frame is gone-straight by rotating the cam cylinder, there is a system what is called step-zoom in which cam grooves corresponding to the zooming area and focusing area are alternately provided in the cam cylinder for moving 2 lens groups, and zooming and focusing are conducted by a one motor.
As the latter system by which the lens frame is directly moved along the guide shaft by using lead screw, it is widely used in the lens barrel in which a collapsible mechanism is not necessary, because the structure can be simple, and as the drive apparatus for directly moving the lens frame by using the motor and lead screw, there are the lead screw for moving one hand lead screw and the lead screw for moving the other hand lead screw, and the moving power is transmitted from one hand lead screw to the other hand lead screw by using a gear or a belt, and the lens drive apparatus by which 2-lens groups are moved by one motor is well known (for example, refer to Patent Document 1).
Further, the lens barrel by which the zooming and focusing are conducted by a single motor when 2 axes on which cam groves are provided, are serially arranged with a play in the rotation direction, and the lens groups engaged with the cam groove of respective grooves are driven, is well known (for example, refer to Patent Document 2).
[Patent Document 1] JP-A No. 2001-124974 (Hereinafter, JP-A refers to Japanese Patent Publication Open to Public Inspection)
[Patent Document 2] JP-A No. 4-317015
However, in the system called step-zoom, although the zooming and focusing can be conducted when the plurality of lens groups are moved along the optical axis by one motor, at the time of zooming, the focal distance is changed stepwise, and continuous tiny step focal distance change can not be conducted, further, because the shape of cam is complex, and because cylindrical cam cylinder is arranged outside the lens groups, there is a problem that the size becomes large in the diameter direction and the size is increased.
Further, in the lens drive apparatus written in the Patent Document 1, because it can be applied for zooming, however the focusing can not be conducted, the drive source such as the motor for focusing is separately necessary, and when it is applied for the lens barrel, there is a problem that, in addition to the cost-up, the size is increased.
Further, in the structure of the lens barrel written in Patent Document 2, the play becomes an amount within one rotation of the axis, and it is difficult that the moving amount of lens groups or the accuracy (resolving power) for focusing is secured enough.